Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 290346

Area Forecast Discussion
National Weather Service Portland OR
845 PM PDT Sun May 28 2017

.SYNOPSIS...Cooler for Monday, with a lot more in way of low clouds
in the morning into early afternoon. Approaching low pressure from
the west will bring increasing southerly flow aloft. This will result
in threat of showers, and afternoon/evening thunderstorms over the
Cascades and foothills. Otherwise, back to typical late May/early
June weather, with partly to mostly cloudy skies and near seasonable


.SHORT TERM...(Tonight through Wednesday). Skies mostly clear from
the Coast mountains eastward to the Cascades this evening. But, that
will change tonight thanks to increasing onshore flow. This evident
by the cooler temperatures, with 8 pm temperatures in the upper 50s
to lower 60s across the lower Columbia and Cowlitz Valley, as well as
the south Willamette Valley. This cooler marine air will cool further
tonight, allowing marine clouds to spread across much of the interior
after midnight. Did boost cloud extent in forecast grids and coverage
for tonight and Mon. Enough that the clouds will be breaking up Mon
afternoon. Will chance precip to occasional drizzle for coast and
coast mtns, and include patchy drizzle further inland into Mon am.

Also, with the increased cloud cover on Mon, and decent onshore flow,
will drop Mon highs a bit more, with lower to mid 70s over much of
the interior, with a few spots peaking in the upper 70s around the
Portland/Vancouver metro. But, that may even be too optimistic.
Current models still indicated thermal trough will become much more
established in the Columbia Basin Mon afternoon. So, will put bit
more wind in the eastern Columbia Gorge and Hood River zones for
later Mon afternoon and evening, as pressure gradients increase.

Thunderstorm chances will increase in the Cascades the next 2 days as
moisture increases and temperatures cool aloft. Will have to watch
for any drift of these thunderstorms into the valley based on backed
flow through the mid levels.                               /Rockey.

.LONG TERM...(Wednesday Night through Saturday) The Tuesday trough
will bring a cool down to the area starting Tuesday with more
seasonable weather through the remainder of the week. Additional
shortwaves will move through the area Thursday and Friday which will
increase shower chances. The forecast becomes a lot more uncertain
towards next weekend as the ECMWF trys to cut off an upper low
overhead while the GFS strengthens a ridge into the area. Went with a
consensus blend today and will work to add more details this week as
things become more clear. /Bentley


.AVIATION...Southwest onshore marine push underway this evening.
The marine layer is deeper than Saturday with cigs around
1000-1500 feet along the coast. Cloud tops along the coast
estimated around 2500-3000 ft. MVFR cigs will fill most of the
interior late tonight and early Monday starting in the south and
working northward. MVFR cigs will also work up the lower Columbia
river to the KPDX area. Clouds will dissipate over the interior
through midday Mon while coastal areas likely to remain cloudy.

KPDX AND APPROACHES...VFR through most of tonight but MVFR cigs
around 1500 ft likely after 12Z Mon or so, but chances start
increasing after about 09Z. MVFR cigs continue through 18Z the
trending to VFR.  /mh

.MARINE...Quiet conditions continue with northwesterly winds
below 20 kt through at least the middle of this week and likely
longer. Seas around 4 ft and will continue through at least the
middle of the week. Weak system appears likely later this week,
with winds shifting to southerly on Wednesday, but winds right
now appear to remain below 20 kt with this system as well. Seas
may come up a foot or two with this system, but should be little

Next chance for SCA conditions will be next weekend as a broad
upper-level ridge builds over the NE Pacific, setting up a
summer-like gusty northerly wind pattern over our waters. -McCoy




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This discussion is for Northwest Oregon and Southwest Washington
from the Cascade crest to 60 nautical miles offshore. The area is
commonly referred to as the forecast area. is the U.S. government's official web portal to all federal, state and local government web resources and services.